Following are a number of back-translations as well as a sample translation for translators of Isaiah 30:29:

• Kupsabiny: “You shall sing
  like when one sings at night
  at a great feast.
  You shall rejoice like people who are strutting
  blowing flutes
  going to the Mountain of God
  that is the shield of Israel.” (Source: Kupsabiny Back Translation)
• Newari: “But you God’s people will be happy Then, like you do to observe a holy family festival
  you will sing a song in the night.
  It will be like going up to the mountain of the LORD,
  the rock of Israel,
  playing the flute [and] rejoicing,
  your hearts will also be filled with joy.” (Source: Newari Back Translation)
• Hiligaynon: “But you (plur.) the people of God will-sing like what you (plur.) are-doing at night-time celebrating the feast to honor the LORD. You (plur.) will-rejoice like the people who are-marching in the sound of flute while they go to the Mountain of the LORD to worship him who is the rock the place-of-refuge of Israel.” (Source: Hiligaynon Back Translation)
• English: “But his people will sing joyfully
  like they sing during the nights when they celebrate a holy festival.
  They will be very joyful,
  like a large group of his people are joyful when they go up to Zion Hill in Jerusalem,
  along with men playing flutes
  when they are all going there to worship Yahweh.
  He is like a huge rock under which we Israeli people are safe.” (Source: Translation for Translators)